Capacitive-loaded jumper cables, shunt capacitance units and related methods for enhanced power delivery to remote radio heads

ABSTRACT

Tower systems suitable for use at cellular base stations include a tower, an antenna mounted on the tower, a remote radio head mounted on the tower and a power supply. A power cable having a power supply conductor and a return conductor is connected between the power supply and the remote radio head. A shunt capacitance unit that is separate from the remote radio head that is electrically coupled between the power supply conductor and the return conductor of the power cable.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §120 as acontinuation of U.S. patent application Ser. No. 14/619,211, filed Feb.11, 2015, which in turn claims priority under 35 U.S.C. §120 as acontinuation-in-part of U.S. patent application Ser. No. 14/487,329,filed Sep. 16, 2014, which in turn claims priority from U.S. ProvisionalPatent Application Ser. No. 61/878,821, filed Sep. 17, 2013, thedisclosure of each of which is hereby incorporated herein by referenceas if set forth in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to remote radio heads, and moreparticularly to delivering power to remote radio heads at the top ofantenna towers and/or in other locations that are remote from a powersupply.

BACKGROUND

Cellular base stations typically include, among other things, a radio, abaseband unit, and one or more antennas. The radio receives digitalinformation and control signals from the baseband unit and modulatesthis information into a radio frequency (“RF”) signal that is thentransmitted through the antennas. The radio also receives RF signalsfrom the antenna and demodulates these signals and supplies them to thebaseband unit. The baseband unit processes demodulated signals receivedfrom the radio into a format suitable for transmission over a backhaulcommunications system. The baseband unit also processes signals receivedfrom the backhaul communications system and supplies the processedsignals to the radio. A power supply is provided that generates suitabledirect current (“DC”) power signals for powering the baseband unit andthe radio. The radio is often powered by a (nominal) −48 Volt DC powersupply.

In order to increase coverage and signal quality, the antennas in manycellular base stations are located at the top of a tower, which may be,for example, about fifty to two hundred feet tall. In early cellularsystems, the power supply, baseband unit and radio were all located inan equipment enclosure at the bottom of the tower to provide easy accessfor maintenance, repair and/or later upgrades to the equipment. Coaxialcable(s) were routed from the equipment enclosure to the top of thetower that carried signal transmissions between the radio and theantennas. However, in recent years, a shift has occurred and the radiois now more typically located at the top of the antenna tower andreferred to as a remote radio head (“RRH”). Using remote radio heads maysignificantly improve the quality of the cellular data signals that aretransmitted and received by the cellular base station, as the use ofremote radio heads may reduce signal transmission losses and noise. Inparticular, as the coaxial cable runs up the tower may be 100-200 feetor more, the signal loss that occurs in transmitting signals at cellularfrequencies (e.g., 1.8 GHz, 3.0 GHz, etc.) over the coaxial cable may besignificant. Because of this loss in signal power, the signal-to-noiseratio of the RF signals may be degraded in systems that locate the radioat the bottom of the tower as compared to cellular base stations whereremote radio heads are located at the top of the tower next to theantennas (note that signal losses in the cabling connection between thebaseband unit at the bottom of the tower and the remote radio head atthe top of the tower may be much smaller, as these signals aretransmitted at baseband frequencies or as optical signals on a fiberoptic cable and then converted to RF frequencies at the top of thetower).

FIG. 1 schematically illustrates a conventional cellular base station 10in which the radios are implemented as remote radio heads. As shown inFIG. 1, the cellular base station 10 includes an equipment enclosure 20and a tower 30. The equipment enclosure 20 is typically located at thebase of the tower 30, and a baseband unit 22 and a power supply 26 arelocated within the equipment enclosure 20. The baseband unit 22 may bein communication with a backhaul communications system 28. A pluralityof remote radio heads 24 and a plurality of antennas 32 (e.g., threesectorized antennas 32) are located at the top of the tower 30. Whilethe use of tower-mounted remote radio heads 24 may improve signalquality, it also requires that DC power be delivered to the top of thetower 30 to power the remote radio heads 24.

A fiber optic cable 38 connects the baseband unit 22 to the remote radioheads 24, as fiber optic links may provide greater bandwidth and lowerloss transmissions. A power cable 36 is also provided for delivering theDC power signal up the tower 30 to the remote radio heads 24. The powercable 36 may include a first insulated power supply conductor and asecond insulated return conductor. The fiber optic cable 38 and thepower cable 36 may be provided together in a hybrid power/fiber opticcable 40 (such hybrid cables that carry power and data signals up anantenna tower are commonly referred to as “trunk” cables). The trunkcable 40 may include a plurality of individual power cables that eachpower a respective one of the remote radio heads 24 at the top of theantenna tower 30. The trunk cable 40 may include a breakout enclosure 42at one end thereof (the end at the top of the tower 30). Individualoptical fibers from the fiber optic cable 38 and individual conductorsof the power cable 36 are separated out in the breakout enclosure 42 andconnected to the remote radio heads 24 via respective breakout cords 44(which may or may not be integral with the trunk cable 40) that runbetween the remote radio heads 24 and the breakout enclosure 42.Stand-alone breakout cords 44 are typically referred to as “jumpercables” or “jumpers.” Coaxial cables 46 are used to connect each remoteradio head 24 to a respective one of the antennas 32.

The DC voltage of a power signal that is supplied to a remote radio head24 from the power supply 26 over a power cable 36 and breakout cord 44may be determined as follows:

V _(RRH) =V _(PS) −V _(Drop)   (1)

where V_(RRH) is the DC voltage of the power signal that is delivered tothe remote radio head 24, V_(PS) is the DC voltage of the power signalthat is output by the power supply 26, and V_(Drop) is the decrease inthe DC voltage that occurs as the DC power signal traverses the powercable 36 and breakout cord 44 that connect the power supply 26 to theremote radio head 24. V_(Drop) may be determined according to Ohm's Lawas follows:

V _(Drop) =I _(RRH) *R _(Cable)   (2)

where R_(cable) is the cumulative electrical resistance (in Ohms) alongthe power supply and the return conductors of the power cable 36 andbreakout cord 44 that connect the power supply 26 to the remote radiohead 24, and I_(RRH) is the average current (in Amperes) flowing throughthe power cable 36 and breakout cord 44 to the remote radio head 24. Asis readily apparent from Equation 2, as the current I_(RRH) drawn by aremote radio head 24 increases, the voltage drop V_(Drop) along thepower cable 36 will increase as well. The voltage drop V_(Drop) ofEquation 2 is also referred to herein as the I*R voltage drop.

The power cables 36 and breakout cords 44 employed in cellular basestations typically use copper power supply and return conductors (oralloys thereof) that have physical properties which are familiar tothose skilled in the art. One important property of these conductors istheir electrical resistance. The electrical resistance of a conductor ofthe power cable 36 (or breakout cord 44) is inversely proportional tothe diameter of the conductor (assuming a conductor having a circularcross-section). Thus, the larger the diameter of the conductors (i.e.,the lower the gauge of the conductor), the lower the resistance of thepower cable 36. Copper resistance is specified in terms of unit length,typically milliohms (mΩ)/ft; as such, the cumulative electricalresistance R_(cable) of the power cable 36 and the breakout cord 44increases with the lengths of the cable 36 and the breakout cord 44.Typically, the breakout cords 44 are much shorter than the power cables36, and hence the power cable 36 is the primary contributor to thecumulative resistance. Thus, the longer the power cable 36, the higherthe voltage drop VT_(Drop). This effect is well understand and istypically accounted for by engineering and the system architects.

Remote radio heads 24 are typically designed to operate properly ifsupplied with a DC power signal having a voltage within a specifiedrange. Conventionally, the power supply 26 at the base of the tower 30will be set to output a DC power signal having a fixed voltage V_(PS).As V_(Drop) is a function of the current I_(RRH) that is supplied to theremote radio head 24 (see Equation 2 above), the voltage V_(RRH) of thepower signal that is delivered to the remote radio head 24 will changewith variation in the current I_(RRH) drawn by the remote radio head 24due to variation in the voltage drop V_(Drop). If V_(Drop) becomes toolarge, then the voltage of the power signal that is supplied to theremote radio head 24 may fall below the minimum voltage that isnecessary to properly power the remote radio head 24.

SUMMARY

Some embodiments of the present invention are directed to jumper cablesfor a cellular base station. These jumper cables include a cable segmentthat has a power supply conductor and a return conductor that areenclosed within a cable jacket and electrically insulated from eachother, and first and second connectors that are terminated onto opposingfirst and second ends of the cable segment. These jumper cables furtherinclude a shunt capacitance unit that is connected between the powersupply conductor and the return conductor, the shunt capacitance unitincluding at least one capacitor that is coupled between the powersupply conductor and the return conductor.

In some embodiments, wherein the at least one capacitor may be anon-polar electrolytic capacitor or at least two polar electrolyticcapacitors. The at least one capacitor may have a capacitance of atleast 400 microfarads. The shunt capacitance unit may be configured toreduce a voltage drop at the remote radio head due to a spike in adirect current power supply signal carried by the jumper cable.

In some embodiments, the shunt capacitance unit may include a housingthat has first and second apertures that the cable segment extendsthrough, and the at least one capacitor may be mounted within thehousing. In such embodiments, the housing may be filled with epoxy thatis configured to provide environmental protection to the at least onecapacitor and the power supply and return conductors. In otherembodiments, the shunt capacitance unit may be included in at least oneof the first connector and the second connector. In still otherembodiments, the shunt capacitance unit may be enclosed within the cablejacket.

In some embodiments, the jumper cable may also include a fuse circuitthat is coupled in series with the at least one capacitor between thepower supply conductor and the return conductor. The jumper cable mayalso include at least one optical fiber within the jacket. The jumpercable may be used at a cellular base station to connect a breakoutenclosure that terminates a trunk cable that is routed up an antennatower to a remote radio head.

Pursuant to further embodiments of the present invention, methods ofoperating a cellular base station are provided in which a direct current(“DC”) power signal is output from a power supply, and this DC powersignal is supplied to a remote radio head that is mounted remotely fromthe power supply over a trunk cable and a jumper cable that areconnected in series, the jumper cable including a power supplyconductor, a return conductor and a shunt capacitance unit that iscoupled between the power supply conductor and the return conductor. Avoltage level of the DC power signal that is output from the powersupply is adjusted so that the DC power signal that is delivered to theremote radio head has a substantially constant voltage notwithstandingvariation in a current level of the DC power signal that is output fromthe power supply

In some embodiments, the power supply may be a programmable powersupply, and information may be input to the power supply from which thevoltage level of the DC power signal that is output from the powersupply can be determined that will provide the DC power signal at thefirst end of the power cable that has the substantially constantvoltage. The method may further include measuring the current level ofthe DC power signal that is output from the power supply, where thevoltage level of the DC power signal that is output by the power supplyis automatically adjusted in response to changes in the measured currentlevel of the DC power signal that is output from the power supply toprovide the DC power signal at the first end of the power cable that hasthe substantially constant voltage. The method may also includedetermining a resistance or an impedance of the power cabling connectionbetween the power supply and the shunt capacitance unit by transmittingan alternating current signal over the power cabling connection andthrough the shunt capacitance unit. The substantially constant voltagemay be a voltage that exceeds a nominal power signal voltage of theremote radio head and which is less than a maximum power signal voltageof the remote radio head.

Pursuant to still further embodiments of the present invention, shuntcapacitance units for cellular base stations are provided that include ahousing, a first connector coupled to the housing, the first connectorincluding a first power supply conductor and a first return conductor,and a second connector coupled to the housing, the second connectorincluding a second power supply conductor that is electrically connectedto the first power supply conductor and a second return conductor thatis electrically connected to the first return conductor. These shuntcapacitance units also include at least one capacitor electricallycoupled between the first power supply conductor and the first returnconductor

In some embodiments, the shunt capacitance unit may further include afuse circuit coupled in series with the at least one capacitor betweenthe first power supply conductor and the first return conductor. The atleast one capacitor may be a non-polar electrolytic capacitor or atleast two polar electrolytic capacitors. The at least one capacitor mayhave a capacitance of at least 400 microfarads.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a simplified, schematic view of a conventional cellular basestation in which several remote radio heads are located at the top of anantenna tower.

FIGS. 2A and 2B are graphs illustrating the DC voltage and current,respectively, of a DC power signal as function of time at a remote radiohead under steady state conditions.

FIG. 3A is a graph illustrating the current of a DC power signal asfunction of time at a remote radio head during a current spike event.FIG. 3B is a graph illustrating how the DC voltage of the power signalvaries as function of time at the remote radio head due to the I*Rvoltage drop in response to the current spike of FIG. 3A. FIG. 3C is agraph illustrating the DC voltage of the DC power signal as function oftime at the remote radio head in response to the current spike of FIG.3A when both the I*R and the dI/dt voltage drops are taken into account.

FIG. 4 is a graph illustrating the DC voltage of the DC power signal asfunction of time at a remote radio head in response to the current spikeof FIG. 3A when both the I*R and the dI/dt voltage drops are taken intoaccount when a shunted capacitance is used to dampen the effect of thedI/dt drop.

FIGS. 5A through 5C are circuit diagrams that illustrate examplelocations where a shunt capacitance unit may be place along a powercable that delivers a DC power signal up an antenna tower to a remoteradio head.

FIGS. 6A and 6B are schematic diagrams of cellular base stations thatillustrate example locations where shunt capacitance unit may be locatedat the top of the antenna tower.

FIG. 7 is a schematic diagram illustrating a cellular base stationaccording to further embodiments of the present invention that uses apower cable having shunt capacitance units built into the power cable.

FIG. 8 is a perspective view of an end portion of a hybrid power/fiberoptic cable that may be used to implement the trunk cable of FIG. 7.

FIG. 9 is a schematic block diagram of a cellular base station accordingto further embodiments of the present invention.

FIG. 10 is a schematic drawing illustrating how a jumper cable may beused to connect a junction enclosure such as a breakout box of a trunkcable or a stand-alone enclosure to a remote radio head.

FIGS. 11A and 11B are a partially-exploded perspective view and aperspective view, respectively, of a shunt capacitance unit according tocertain embodiments of the present invention that may be included in thejumper cable of FIG. 10.

FIG. 11C is a circuit diagram illustrating how the shunt capacitanceunit of the jumper cable of FIGS. 11A-B is electrically connectedbetween the power supply and return conductors of the jumper cable.

FIGS. 12A and 12B are side views of capacitive-loaded jumper cablesaccording to further embodiments of the present invention.

FIG. 13 is a schematic view of an inline connector that includes a shuntcapacitance unit according to certain embodiments of the presentinvention.

FIG. 14 is a block diagram of portions of a cellular base stationaccording to embodiments of the present invention that includes acapacitive-loaded jumper cable that is used to reduce voltage drop andto measure the resistance of the power cabling connection in order toset the output of a variable power supply that powers a remote radiohead.

DETAILED DESCRIPTION

As discussed above, when remote radio heads are used in a cellular basestation, a voltage drop occurs along the power cables that connect apower supply at the base of the antenna tower to the remote radio headsat the top of the antenna tower. This voltage drop may cause severalproblems, as explained below.

First, as the current drawn by one of the remote radio heads increases,the voltage drop V_(Drop) on the individual power cable(s) that connectthe power supply to the remote radio head likewise increases.Consequently, the voltage of the power signal that is supplied to theremote radio head may, if the voltage drop becomes too large, fall belowthe minimum voltage that is necessary to properly power the remote radiohead. Thus, for a power cable having copper conductors of a fixed size,the voltage drop V_(Drop) may effectively limit the length of the powercable that may be used. While this limitation on the length of the powercable may be overcome by using larger conductors in the power cable, theuse of larger conductors results in increased material and installationcosts, increased loading on the tower and various other disadvantages.

Second, the voltage drop along the power cable also increases the costof running the remote radio head, as power is lost when delivering thepower signal to the remote radio head, and the amount of power lost is afunction of the current running through the power cable. In particular,the power that is lost (P_(Loss)) in delivering the power signal to theremote radio head over a power cable may be calculated as follows:

P _(Loss) =V _(Drop) *I _(RRH)   (3)

where V_(Drop)=the average voltage drop in Volts along the power cable.Since antenna towers for cellular base stations may be hundreds of feettall and the voltage and currents required to power each remote radiohead may be quite high (e.g., about 50 Volts at about 20 Amperes ofcurrent), the power loss that may occur along the hundreds of feet ofcabling may be significant.

Third, another physical property of the power cable that can result in avoltage drop is the inductance per unit length of the conductors of thecable. In particular, the cumulative inductance of the conductors of thepower cable can produce a voltage drop that is expressed as:

V _(dI/dt Drop) =L*(dI/dt)   (4)

where L is the cumulative inductance of the conductors and dI/dt is therate of change in current flowing through the conductors with respect totime. Herein, V_(dI/dt Drop) is referred to as the “dI/dt voltage drop.”Accordingly, not only is the voltage drop impacted by changes in current(see Equation 2), it is also impacted by how quickly the current changes(see Equation 4). Examples of scenarios where the current drawn by aremote radio head may change quickly (a “current spike”) such that theDI/dt voltage drop can impact performance are (1) when multiple handsetsconnect and demand high speed data simultaneously and (2) when theremote radio head is turned off or on, or from idle to operational.While this voltage drop typically only lasts for a period on the orderof about 1-20 milliseconds, this period is long enough such that rapidcurrent spikes may lead to large V_(dI/dt Drop) values (e.g., as much as5 Volts) which have the potential to impact the performance of a remoteradio head.

Pursuant to embodiments of the present invention, various methods areprovided that may reduce the impact of the above-described voltagedrops. These techniques may be used individually or together to improvethe performance of cellular base stations that use remote radio headsthat are mounted atop antenna towers. It will also be appreciated thatcellular base stations exist where the remote radio heads and antennasare mounted in locations remote from the baseband equipment and powersupply other than towers such as, for example, remote radio heads andantennas that are mounted on rooftops, atop utility poles, in subwaytunnels and the like. It will be appreciated that the techniquesdescribed herein are equally applicable to these “non-tower” remotelocations for the remote radio heads. Thus, while embodiments of thepresent invention are described below with reference to tower-mountedremote radio heads, it will be appreciated that all of the embodimentsdescribed below may be implemented in cellular base stations that placethe remote radio heads in other locations such as on rooftops, atoputility poles and in tunnels or other locations that are remote from thepower supply and baseband equipment.

For example, in some embodiments, a shunt capacitance unit such as, forexample, a capacitor, may be provided between the two conductors of apower cable that is used to provide a DC power signal to a remote radiohead. This shunt capacitance unit may reduce the dI/dt voltage drop thatwould otherwise occur in response to current spikes. In someembodiments, these shunt capacitance units may be integrated into apower cable or a trunk cable that includes a plurality of individualpower cables that are used to provide power to a plurality of remoteradio heads on an antenna tower. In other embodiments, the shuntcapacitance unit may be incorporated into jumper cables that connectremote radio heads to a junction enclosure or to a breakout enclosure ofa power cable. In still other embodiments, the shunt capacitance unitmay be incorporated into an inline connector that may be connected to,for example, a jumper cable. The shunt capacitance units may, in someembodiments, be sized based on, for example, the length of the powercable and the resistance per unit length of the power supply and returnconductors included in the power cable.

In some embodiments, the shunt capacitance units may be used inconjunction with a programmable power supply that is configured to (1)sense the current being drawn by the remote radio head (or anothersuitable parameter) and (2) adjust the voltage of the power signal thatis output by the power supply to substantially maintain the voltage ofthe power signal that is supplied to the remote radio head at or near adesired value. This desired voltage value may be, for example, a valuethat is close to the maximum voltage for the power signal that may beinput to the remote radio head. In some embodiments, the programmablepower supply may set the voltage of the DC power signal that is outputby the power supply based on the resistance of the power cable and thecurrent of the power signal that is output from the power supply so thatthe voltage of the power signal at the top of the tower will besubstantially maintained at a desired level. The resistance of the powercable may, for example, be input to the power supply, calculated basedon information that is input to the power supply, or measured. As thecurrent drawn by the remote radio head varies, the programmable powersupply may adjust the voltage of its output power signal to a voltagelevel that will deliver a power signal to the remote radio head that isat or near the maximum voltage for a power signal that may be input tothe remote radio head. As shown by Equation (5) below, which expandsEquation (3), the power loss varies as the square of the current drawnby the remote radio head. By increasing the voltage of the signal thatis delivered to the remote radio head, the current I_(RRH) of the powersignal is correspondingly reduced, thereby reducing the power loss. As atypical remote radio head may require about a kilowatt of power and mayrun 24 hours a day, seven days a week, and as a large number of remoteradio heads may be provided at each cellular base station (e.g., threeto twelve), the power savings may be significant.

P _(Loss) =V _(Drop) *I _(RRH)=(I _(RRH) *R _(Cable))*I _(RRH) =I _(RRH)² *R _(Cable)   (5)

While the above-discussed programmable power supply will alter thevoltage of the power signal that it outputs in response to the currentdrawn by the remote radio head, the change in the voltage of the outputpower signal may lag behind the change in current. Thus, even whenprogrammable power supplies are used, dI/dt losses may still arise thatmay degrade the performance of the remote radio head. Thus, in someembodiments, both programmable power supplies and shunt capacitanceunits may be used to counter the negative effects of both I*R and dI/dtvoltage drops.

Using a capacitor to help maintain the voltage level of a signal duringa spike in current is known in the art. Moreover, commercially availableremote radio heads may include an internal bulk capacitance across theinput terminals for the power supply leads that is used to reduce rippleand noise on the DC power signal line. However, it is not believed thatappreciation of the impact of dI/dt voltage drops on remote radio headperformance is well understood, nor is it believed to be understood thebenefits that may accrue by providing, for example, a capability toprovide a variable amount of shunt capacitance between the leads of apower cable for a remote radio head where the shunt capacitance unit maybe sized based on the length of the power cable, the cumulativeresistance of the conductors of the power cable and/or various otherfactors such that the shunt capacitance unit may be designed to overcomethe problem of dI/dt voltage drops. According to some embodiments, theshunt capacitance units may be integrated directly into the power cable,into a jumper cable, or into an inline connector that is connected tothe jumper cable.

Embodiments of the present invention will now be discussed in moredetail with reference to FIGS. 2-14, in which example embodiments of thepresent invention are shown.

As noted above, pursuant to embodiments of the present invention, powercables, jumper cables and inline connectors having relatively largeshunt capacitance units may be provided that may be used to maintain thevoltage of the power signal delivered to a remote radio head at or abovea desired minimum level during current spikes. The effect of theinclusion of a large shunt capacitance on the voltage of the powersignal delivered to the remote radio head is illustrated in FIGS. 2-4.

FIGS. 2A and 2B illustrate the power signal received at a remote radiohead under steady state conditions. In particular, FIG. 2A is a graphplotting the DC voltage of the power signal (V_(RRH)) delivered to aremote radio head as function of time when the remote radio head isoperating under steady state conditions, and FIG. 2B is a graph plottingthe current of the power signal (I_(RRH)) drawn by the remote radio headas function of time during such steady state conditions. As shown inFIGS. 2A-2B, under such steady state conditions, the voltage V_(RRH) andthe current I_(RRH) may remain constant.

FIGS. 3A-3C illustrate how the voltage and current of the power signalat the remote radio head change in response to a current spike. Inparticular, FIG. 3A illustrates a current spike which may occur in thepower signal when the current requirements of the remote radio head areincreased. As shown in FIG. 3A, the current spike may be approximated asa step function. Such a current spike may result, for example, ifmultiple carriers key up transmission simultaneously. Assuming that thepower supply is outputting a power signal V_(PS) having a constantvoltage, FIG. 3B shows the effect that the increased current draw willhave on the voltage of the power signal V_(RRH) at the remote radiohead. Specifically, as shown in FIG. 3B, the increased current draw willresult in a decrease in the voltage of the power signal V_(RRH) at theremote radio head based on Ohm's law. The graph of FIG. 3C illustrateshow the dI/dt drop may further impact the voltage of the power signalV_(RRH) supplied to the remote radio head. As shown in FIG. 3C, thedI/dt voltage drop may result in a temporary deep decrease in thevoltage V_(RRH) that gradually recovers to the new steady state voltagethat applies. The broken line in FIG. 3C indicates the voltage levelwhere the power signal may be inadequate to properly power the remoteradio head. As shown in FIG. 3C, the dI/dt voltage drop may besufficient in some cases to cause a remote radio head to temporarilymalfunction due to an insufficient voltage level for the power signal.

FIG. 4 is a graph illustrating how a shunt capacitance unit may be usedto dampen the effect of the dI/dt voltage drop that is shown in FIG. 3C.As shown in FIG. 4, the shunt capacitance unit may dampen the effect ofthe current spike on the voltage V_(RRH). The voltage spike of FIG. 3Cis largely dissipated by the shunt capacitance unit, such that thevoltage level V_(RRH) does not drop below the broken line that indicatesoperational problems with the remote radio head. The shunt capacitanceunit effectively acts as an auxiliary power supply that helps maintainthe voltage by discharging the stored charges during the current spikeevent. Once steady state conditions are reached, the shunt capacitanceunit may recharge to be available to dampen the effect of the nextcurrent spike. By including the shunt capacitance unit, undesirableevents (e.g., the remote radio head shutting down) that the unwantedvoltage spike might otherwise cause can be reduced or prevented.

FIGS. 5A-5C are circuit diagrams that illustrate example locations wherea shunt capacitance unit 48 may be placed along a power cable 36 thatdelivers a power signal up an antenna tower 30 to a remote radio head24. In each of FIGS. 5A-5C, a power supply 26 is connected via a powercable 36 to a remote radio head 24 that is mounted on an antenna tower30. As shown in each of FIGS. 5A-5C, the power cable 36 for each remoteradio head 24 may comprise a power supply conductor 36-1 and a returnconductor 36-2. The conductors 36-1, 36-2 may each be modelled as aplurality of inductors that are disposed in series. In the embodiment ofFIG. 5A, the shunt capacitance unit 48 is inserted between the powersupply conductor 36-1 and the return conductor 36-2 near the powersupply 26 (i.e., at the base of the tower 30). As an alternative, FIG.5B shows that shunt capacitance unit 48 can be inserted as a series ofshunt capacitors 48 that are interposed at different points along thepower supply conductor 36-1 and the return conductor 36-2. FIG. 5C showsthat shunt capacitance unit 48 can be inserted between the power supplyconductor 36-1 and the return conductor 36-2 near the remote radio head24 at or near the top of the tower 30. While FIGS. 5A-5C show a singlepower cable 36 connecting the power supply 26 to the remote radio head24 to provide a simplified example, it will be appreciated that moretypically the end of the power cable 36 at the top of the antenna tower30 terminates into a junction enclosure or includes an integratedbreakout enclosure, and jumper cables are connected between thisenclosure and each remote radio head 24 that carry power and datasignals between the enclosure and each remote radio head 24.

In some embodiments such as the embodiment shown in FIG. 5C, the shuntcapacitance unit 48 is placed very close to the remote radio head 24.FIGS. 6A and 6B identify two locations near a remote radio head 24 whichmay be considered both accessible and functional as locations for theshunt capacitance unit 48. As shown in FIG. 6A, the tower 30 may includea junction enclosure 50 (which is sometimes referred to as a “breakoutbox”) that is positioned adjacent a remote radio head 24 near the top ofthe tower 30. The junction enclosure 50 typically includes a bus bar,fiber breakout units, and the like, and has externally accessibleconnectors. The remote radio head 24 is connected to the breakout box 50via a breakout cord 44. A power supply 26 is connected to the breakoutbox 50 via the power cable 36 (which may be a hybrid power/fiber optictrunk cable 40). As shown in FIG. 6A, one exemplary location for theshunt capacitance unit 48 is inside or at the breakout box 50, whichwould be located at a relatively long distance up the tower 100. In FIG.6B, a cellular base station having the same components as the cellularbase station of FIG. 6A is shown, with the exception that the shuntcapacitance unit 48 is connected at the input of the remote radio head24. In the embodiment of FIG. 6B, shunt capacitance unit 48 may, forexample, be included in an inline connector module. FIG. 13 illustratessuch an inline connector module according to embodiments of the presentinvention. The example locations for the shunt capacitance units 48illustrated in FIGS. 6A and 6B are relatively accessible to technicians.

FIG. 7 is a schematic block diagram illustrating a cellular base station100 according to further embodiments of the present invention thatincludes shunt capacitance units in a power cable 136 that supplies DCpower signals from a power supply 26 to a plurality of remote radioheads 24. In the example of FIG. 7, a total of three remote radio heads24 are mounted on an antenna tower 30. The power cable 136 includesthree pairs of insulated copper conductors 136A-136C (i.e., threeindividual power cables 136A-136C are included in the composite powercable 136) that are used to deliver the DC power signals from the powersupply 26 to the respective remote radio heads 24. Each pair ofinsulated copper conductors 136A-136C includes a power supply conductor136-1 and a return conductor 136-2. The power supply 26 includes threeoutputs 27A-27C. One end of each of the individual power cables136A-136C is connected to a respective one of the outputs 27A-27C onpower supply 26, while the other end of each of the individual powercables 136A-136C is connected to a respective one of the remote radioheads 24. The three outputs 27A-27C on the power supply 26 areindependent from each other and may each deliver a power signal thatmeets the power needs of a respective one of the remote radio heads 24.Thus, through the outputs 27, the power supply 26 may provide threeindependent power signals having voltage and current characteristicsthat are suitable for meeting the instantaneous power requirements ofeach of the remote radio heads 24.

FIG. 8 is a schematic diagram illustrating a trunk cable assembly 200that may used, for example, to implement the power cable 136 (as well asthe fiber optic cable 38) of FIG. 7. The trunk cable assembly 200 ofFIG. 8 comprises a hybrid power/fiber optic cable 210, a first breakoutcanister 230 and a second breakout canister 250. The hybrid power/fiberoptic cable 210 has nine individual power cables 212 (see the callout inFIG. 8, which depicts three of the individual power cables 212), whichmay be stranded together to form a composite power cable 218, and afiber optic cable 220 that includes thirty-six optical fibers 222. Thefiber optic cable 220 may comprise a jacketed or unjacketed fiber opticcable of any appropriate conventional design. The composite power cable218 and the fiber optic cable 220 may be enclosed in a jacket 224. Whileone example hybrid power/fiber optic cable 210 is shown in FIG. 8, itwill be appreciated that any conventional hybrid power/fiber optic cablemay be used, and that the cable may have more or fewer power cablesand/or optical fibers. An exemplary hybrid power/fiber optic cable isthe HTC-24SM-1206-618-APV cable, available from CommScope, Inc.(Hickory, N.C.).

The first breakout canister 230 comprises a body 232 and a cover 236.The body 232 includes a hollow stem 234 at one end that receives thehybrid power/fiber optic cable 210, and a cylindrical receptacle at theopposite end. The cover 236 is mounted on the cylindrical receptacle toform the breakout canister 230 having an open interior. The hybridpower/fiber optic cable 210 enters the body 232 through the stem 234.The composite power cable 218 is broken out into the nine individualpower cables 212 within the first breakout canister 230. Each individualpower cable 212 includes a power supply conductor 214 and a returnconductor 216. The nine individual power cables 212 are routed throughrespective sockets 238 in the cover 236, where they are received withrespective protective conduits 240 such as a nylon conduit that may besufficiently hardy to resist damage from birds. Thus, each individualpower cable 212 extends from the first breakout canister 230 within arespective protective conduit 240. The optical fibers 222 are maintainedas a single group and are routed through a specific socket 238 on thecover 236, where they are inserted as a group into a conduit 242. Thus,the first breakout canister 230 is used to singulated the nine powercables 212 of composite power cable 218 into individual power cables 212that may be run to respective remote radio heads 24, while passing allof the optical fibers 222 to a separate breakout canister 250.

As shown in the inset of FIG. 8, a plurality of shunt capacitance unitsin the form of ceramic capacitors 248 are provided within the firstbreakout canister 230. Each capacitor 248 is connected between the powersupply conductor 214 and the return conductor 216 of a respective one ofthe individual power cables 212. The breakout canister 230 may include aplurality of sockets that each receive one of the capacitors 248. Eachindividual power cable may be physically and electrically connected tothese sockets. For low frequency signals such as a DC power signal, theshunt capacitors 248 appear as an open circuit, and thus the DC powersignal that is carried on each individual power cable 212 will pass bythe respective shunt capacitor 248 to the remote radio heads 24.However, as discussed above, during periods where the current carried byan individual power cable 212 spikes in response to an increased currentrequirement at the remote radio head 24, the shunt capacitor 248 may actakin to an auxiliary power supply to reduce the magnitude of the dI/dtvoltage drop on the DC power signal.

As noted above, the optical fibers 222 pass through the first breakoutcanister 230 as a single unit in conduit 242 which connects to thesecond breakout canister 250. In the second breakout canister 250, thethirty-six optical fibers 222 are separated into nine optical fibersubgroups 252. The optical fiber subgroups 252 are each protected withina respective conduit 254. The second breakout canister 250 may besimilar to the first breakout canister 230, and hence will not bediscussed in further detail. The second breakout canister 250, however,does not include the shunt capacitors 248.

As is known to those of skill in the art, commercially available remoteradio heads may have capacitances across the leads that receive a powercable that powers the remote radio head. However, this capacitance istypically small and may not be sufficient to dampen the dI/dt voltagedrop. By providing power cables such as the hybrid power/fiber opticcable assembly 200 of FIG. 8 that have shunt capacitors 248 integratedinto each individual power cable 212, it is possible to ensure that asufficient shunt capacitance is provided in each instance. For example,as discussed above, voltage drop becomes a more significant issue thelonger the power cable, as I*R based voltage drops increase linearlywith the length of the power cable. Thus, longer power cables are morelikely to experience the situation illustrated in FIG. 3C above wherethe combination of the I*R voltage drop and the dI/dt voltage drop maycause the voltage of the power signal to temporarily dip below someminimum required voltage level, thereby disrupting operation of theremote radio head. By implementing the shunt capacitances within thepower cables—which may be sold in known lengths—the shunt capacitancesmay be appropriately pre-sized to provide a sufficient amount ofcapacitance while not providing excess capacitance that may increase thecost, size and/or weight of the power cable.

Additionally, by implementing the shunt capacitances within the powercable and, more particularly, within a breakout enclosure of the powercable, it is possible to have shunt capacitances that may be sizedappropriately at the time of installation. For example, in someembodiments, the shunt capacitance may be plug-in or screw-in capacitorsthat are connected across the conductors of each power cable so that theappropriately-sized capacitor may be installed in the breakout canisterbased on the specific requirements of the cellular base station.Additionally, since the breakout canisters may be opened up, ifnecessary, after installation, defective or damaged capacitors may bereplaced if needed.

Those of skill in this art will appreciate that the shunt capacitancesused in embodiments of the present invention may be provided in anynumber of forms. For example, a shunt capacitance unit may be in theform of individual components, such as one or more capacitors, or in theform of other physical structures such as parallel conductors separatedby an air gap that may act like a capacitor. The amount of shuntcapacitance provided may vary depending on a number of factorsincluding, for example, the length of the conductors and the diameter ofthe conductors. Generally speaking, the amount of shunt capacitance maybe on the order of hundreds, thousands, tens of thousands, or hundredsof thousands of microfarads in some embodiments.

The benefits that may accrue from using shunt capacitances in the mannerdescribed herein may include the following. From a system perspective,the conductors of a power cable for a remote radio head need not beoversized or overdesigned to compensate for large dI/dt voltage drops;consequently, longer conductor runs utilizing less conductor materialare possible. The use of less conductor material also allows for lighterpower cable assemblies, which can also be advantageous because increasedcurrent demand at the top of the tower is a rapidly developing issue.Moreover, existing tower architectures may be retrofitted with thisapproach with minimal impact to mounted hardware should dI/dt voltagedrops arise as an issue. In particular, embodiments of this inventioncan allow for a variable amount of required capacitance based on, forexample, conductor length, while also allowing the ability to retrofitan existing tower, power cable, or remote radio head architecture.

Pursuant to further embodiments of the present invention, power cablesthat include shunt capacitances may be used in cellular base stationsthat employ programmable power supplies that are used to reduce the I*Rvoltage drop by maintaining the voltages of the power signals at theremote radio heads at or near a maximum voltage for the power signalthat is specified for each remote radio head. Examples of such anembodiment will now be described with reference to FIG. 9.

In particular, FIG. 9 is a schematic block diagram of a cellular basestation 300 according to embodiments of the present invention. As shownin FIG. 3, the cellular base station 300 includes an equipment enclosure20 and a tower 30. A baseband unit 22, a first power supply 326 and asecond power supply 328 are located within the equipment enclosure 20. Aplurality of remote radio heads 24 and plurality of antennas 32 aremounted on the tower 30.

Each remote radio head 24 receives digital information (data) andcontrol signals from the baseband unit 22 over a fiber optic cable 38.Typically, the fiber optic cable 38 will include a plurality of opticalfibers, with two (or more optical fibers) provided for each remote radiohead 24. Each remote radio head 24 modulates the data signals receivedover its respective “uplink” optical fiber into a radio frequency (“RF”)signal at the appropriate cellular frequency that is then transmittedthrough an antennas 32. Each remote radio head 24 also receives RFsignals from an antenna 32, demodulates these signals, and supplies thedemodulated signals to the baseband unit 22 over its respective“downlink” optical fiber that is included in the fiber optic cable 38.The baseband unit 22 processes the demodulated signals received from theremote radio heads 24 and forwards the processed signals to the backhaulcommunications system 28. The baseband unit 22 also processes signalsreceived from the backhaul communications system 28 and supplies thesesignals to the remote radio heads 24. Typically, the baseband unit 22and the remote radio heads 24 each include optical-to-electrical andelectrical-to-optical converters that couple the digital information andcontrol signals to and from the fiber optic cable 38.

The first power supply 326 generates direct current (“DC”) powersignals. The second power supply 328 is a DC-to-DC converter thataccepts the DC power signal output by the first power supply 326 as aninput and outputs a DC power signal having a different voltage. A powercable 336 is connected to the output of the second power supply 328 androuted up the tower 30. The power cable 336 may be a composite powercable that includes multiple individual power cables, namely anindividual power cable for each remote radio head 24. In someembodiments, the fiber optic cable 38 and the power cable 336 may beimplemented together as a hybrid power/fiber optic cable 340 which maybe implemented, for example, using the hybrid power/fiber optic cableassembly 200 of FIG. 8. While the first power supply 326 and the secondpower supply 328 are illustrated as separate power supply units in theembodiment of FIG. 9, it will be appreciated that the two power supplies326, 328 may be combined into a single power supply unit in otherembodiments.

The power supply 328 is a programmable power supply that receives inputDC power signals from power supply 326 and outputs DC power signals toeach of the individual power cables within the power cable 336. Thevoltage of the DC power signal output by the power supply 328 may varyin response to variations in the current of the DC power signal drawnfrom the power supply 328 by the remote radio heads 24 that areconnected to each individual power cable. The voltage of the DC powersignal output by the power supply 328 may be set so that the voltage ofthe DC power signal at the far end of each individual power cable inpower cable 336 (i.e., the end adjacent the remote radio heads 24) ismaintained at or near the maximum specified voltage for the power signalof the remote radio heads 24. This may reduce the power loss associatedwith supplying the DC power signal to the remote radio head 24, since,for a given power level, a higher voltage for the DC power signalcorresponds to a lower current, and lower current values result inreduced power loss. In some embodiments, the programmable power supply328 may be designed to maintain the voltage of the DC power signal at ornear a maximum operating voltage for the power signal that may besupplied to the remote radio head 24.

In some embodiments, the voltage of the DC power signal at the far endof the individual power cables in power cable 336 (i.e., V_(RRH)) may bemaintained at or near a predetermined value by setting the voltage levelof the power signal output by power supply 328 based on (1) the currentof the DC power signal drawn from the power supply (note from Equations1 and 2 that V_(RRH) is a function of I_(RRH)) and (2) the resistanceR_(cable) of the power cable. The programmable power supplies accordingto embodiments of the present invention may be configured to measure,estimate, calculate or receive both values. U.S. patent application Ser.No. 14/321,897 (“the '897 application”), filed Jul. 2, 2014, describesvarious programmable power supplies that may be used to implement theprogrammable power supply 328. The '897 application is incorporated byreference herein in its entirety, and hence further description ofregarding implementation of these programmable power supplies entirewill be omitted. Note that either the resistance or the impedance of thepower cable may be used to set the voltage level of the power signaloutput by power supply 328, and references herein to the “resistance” ofthe power cable are intended to cover both the resistance and/or theimpedance. In other embodiments, a feedback loop may be used to controlthe voltage of the DC power signal output by the DC power supply so thatthe voltage of the DC power signal at the far end of the power cablethat connects the power supply 328 and a remote radio head 24 ismaintained at a desired level. The use of such feedback loops is alsodiscussed in the '897 application.

The use of such programmable power supplies may both reduce power lossesand also reduce the I*R voltage drop, as supplying power signals havingvoltages that are maintained near a maximum acceptable value to eachremote radio head reduces the average current of the power signals,thereby reducing I*R voltage drop. Additionally, the cellular basestations according to embodiments of the present invention may alsoemploy shunt capacitances on each individual power cable in the mannerdescribed above with reference to FIGS. 2-8 to reduce the impact ofdI/dt voltage drops.

Pursuant to further embodiments of the present invention, the shuntcapacitance unit may be incorporated into a jumper cable that connectsto a breakout enclosure of a trunk cable or a separate junctionenclosure to a remote radio head, or may be included in, for example, aninline connector unit that is directly connected to such jumper cables.Such approaches may have advantages over including the shunt capacitanceunit in the trunk cable in certain situations.

As discussed above, trunk cables are often used to transmit power from apower supply and data signals from a baseband unit that are locatedadjacent the bottom of an antenna tower of a cellular base station to ajunction enclosure (or other breakout enclosure or canister) that ismounted near the top of the antenna tower. Typically, the trunk cableincludes a plurality of pairs of power conductors and a plurality ofpairs of optical fibers, where each pair of power conductors is providedto deliver a power signal to a respective one of the remote radio headsmounted at the top of the antenna tower, and each pair of optical fibersis provided to carry the uplink and downlink traffic to a respective oneof the remote radio heads. These pairs of power conductors and opticalfibers are terminated into connectors that are provided in the junctionenclosure. Individual jumper cables may be connected between therespective connectors of the junction enclosure and respective remoteradio heads in order to complete the connections between each remoteradio head and the power supply and baseband equipment at the base ofthe antenna tower. In some cases, separate power jumper cables and fiberoptic jumper cables are provided, while in other cases composite jumpercables that include both optical fibers and power conductors (which areseparately connectorized) may be used to connect each remote radio headto the junction enclosure.

The jumper cables are much shorter in length than the trunk cables, asthe junction enclosure is typically located only a few feet from theremote radio heads, whereas the trunk cable is routed tens or hundredsof feet up the antenna tower. Additionally, the jumper cables includefar fewer components. For example, a power jumper cable may comprise a6-foot cable having two insulated conductors and connectors on eitherend thereof. In contrast, for an antenna tower with nine remote radioheads, which is an increasingly common configuration, the trunk cablemay be 250 feet long, include eighteen insulated conductors, and alsoinclude eighteen optical fibers, along with connectors for each powerconductor and optical fiber. As such, trunk cables are typically farmore expensive than jumper cables.

If the shunt capacitance is implemented in the trunk cable, thenretrofit installations may require replacement of an existing trunkcable, which may be very expensive in terms of both the cost of thetrunk cable and the costs associated with replacing a trunk cable interms of man hours, equipment rental, etc. As noted above, the shuntcapacitance units according to embodiments of the present invention mayalso be subject to failure, particularly as the power cabling oncellular antennas may be subject to lightning strikes and/or othervoltage surges. When such failures occur, it again may be necessary toreplace the cabling or enclosure in which the shunt capacitance unit iscontained. This may be very expensive when the shunt capacitance unit iscontained in the trunk cable or a breakout enclosure thereof. Whilereplacing shunt capacitance units that are contained in a junctionenclosure may not be as expensive from a capital cost viewpoint, openingjunction enclosures at the top of cellular towers is generallydiscouraged for a wide variety of reasons such as safety, environmentalsealing concerns and the like. Thus, while placing shunt capacitanceunits in a trunk cable, trunk cable breakout enclosure and/or junctionenclosure may have various advantages, such as locating the shuntcapacitance unit at a short distance from the associated remote radiohead and sizing the capacitance based on the length of the trunk cable,there may also be various disadvantages with this approach.

Providing jumper cables that have associated shunt capacitance units mayprovide a more efficient and cost-effective way of retrofitting existingcellular base stations to include shunt capacitance units. As notedabove, jumper cables are much less expensive than trunk cables, andhence can be replaced at less cost, even though it may be necessary toreplace a plurality of jumper cables (as a separate jumper cableconnects each remote radio head to the junction enclosure or breakoutenclosure of the trunk cable). Moreover, jumper cables may be easilyreplaced by a technician as they are designed to be connected anddisconnected, and jumper cable replacement does not raise environmentalsealing concerns as does opening a junction enclosure. As any laborperformed at the top of an antenna tower is expensive, the ease withwhich a retrofit may be performed using jumper cables having associatedshunt capacitance units may represent a significant advantage. Theadvantages that jumper cables with associated shunt capacitance unitsprovide for retrofit applications are equally applicable in situationswhere the capacitor of a shunt capacitance unit burns out and must bereplaced.

Additionally, locating the shunt capacitance unit in a jumper cable mayalso place the shunt capacitance unit closer to the remote radio head.As discussed above, this may provide improved performance. Moreover,maintaining an inventory of jumper cables having shunt capacitance unitsmay be far more efficient than maintaining an inventory of trunk cableswith such shunt capacitance units.

Jumper cables having associated shunt capacitance units according toembodiments of the present invention will now be discussed withreference to FIGS. 10-12 and 14.

FIG. 10 is a schematic drawing illustrating how a jumper cable having anassociated shunt capacitance unit according to embodiments of thepresent invention may be used to connect a junction enclosure such as abreakout box of a trunk cable or a stand-alone enclosure to a remoteradio head. As shown in FIG. 10, a trunk cable 410 is terminated into ajunction enclosure 420 at, for example, the top of an antenna tower (notshown). A jumper cable 430-1 connects the junction enclosure 420 to aremote radio head 440. The jumper cable 430-1 includes a cable segment431. The cable segment 431 may include a power supply conductor 432 anda return conductor 433 that are electrically insulated from each other(see FIG. 11A). In some embodiments, the power supply conductor 432 andthe return conductor 433 may each comprise an 8-gauge to a 14-gaugecopper or copper alloy wire. The wire may be a solid wire or may bestranded. Stranded wires may be preferred in some embodiments as theymay increase the flexibility of the jumper cable 430-1. In someembodiments, two stranded 10-gauge wires may be stranded together toform the power supply and/or return conductors 432, 433. The use of twosmaller wires that are stranded together to form the power supply and/orreturn conductor 432, 433 may further enhance the flexibility of thejumper cable 430-1.

A protective jacket 434 may enclose the power supply and returnconductors 432, 433. First and second connectors 435, 436 are terminatedonto either end of the cable segment 431. The first connector 435 isconfigured to connect to a mating connector 422 on the junctionenclosure 420, and the second connector 436 is configured to connect toa mating connector 442 of the remote radio head 440. Typically, theconnector 422 on the junction enclosure 420 and the connector 442 on theremote radio head 440 are identical so that either of connectors 435 and436 may be connected to either of the connectors 422, 442. The jumpercable 430-1 may comprise a power cable that only includes the powersupply and return conductors 432, 433, or alternatively may be a hybridfiber optic-power cable that includes both the power supply and returnconductors 432, 433 along with two or more optical fibers. The jumpercable 430-1 may include an associated shunt capacitance unit 438 thatmay be implemented in a variety of locations. Configuration andoperation of the shunt capacitance unit 438 will be described in furtherdetail below with reference to FIGS. 11A-12B.

In some embodiments, the shunt capacitance unit 438 may be implementedon the jumper cable 430-1 as a sealed unit 500 that is interposed alongthe cable segment 431. FIGS. 11A and 11B are a broken-line perspectiveview and a partially-exploded perspective view, respectively, of anexample embodiment of a sealed unit 500 that may be used to implementthe shunt capacitance unit 438. As shown in FIGS. 11A-11B, the sealedunit 500 may have a housing 510 that includes housing pieces 520, 530.Each housing piece 520, 530 includes a respective cable aperture 522,532 that allows the cable segment 431 to pass through the housing 510.The housing pieces 520, 530 may be formed of, for example, athermoplastic material or anodized aluminium. In the embodiment of FIGS.11A-11B, the shunt capacitance is implemented using a pair ofelectrolytic capacitors 540-1, 540-2 that are connected in seriesbetween the power supply conductor 432 and the return conductor 433. Thecapacitors 540 may have a cylindrical shape and may be physicallypositioned so that a longitudinal axis of each capacitor 540 extendsalong the longitudinal axis of the cable segment 431. In exampleembodiments, the capacitor(s) 540 may have a total capacitance ofbetween 400 and 2500 microfarads. The housing 510 may include a pair ofopenings 524, 534. The first of these openings 524 may be used to injectan environmental sealing element such as an epoxy into the interior ofthe housing 510, and the second of these openings 534 may allow air toescape during the epoxy-fill operation. The epoxy (not shown) may beinjected as a gel and may fill the interior of the housing 510. Theepoxy may dry upon exposure to air into a hardened, air and waterimpermeable solid that fills the housing 510. Caps (not shown) may beplaced over the openings 524, 534 in some embodiments, while in otherembodiments the openings 524, 534 may remain uncovered.

The capacitors 540 may comprise, for example, non-polar electrolyticcapacitors. The use of non-polar capacitors 540 may allow the jumpercable 430-1 to be installed in either direction between the junctionenclosure 420 and the remote radio head 440. In other words, if thejumper cable 430-1 is implemented using non-polar capacitors 540, thenconnector 435 of jumper cable 430-1 may be mated to either the matingconnector 422 on the junction enclosure 420 or to the mating connector442 of the remote radio head 440 and the jumper cable 430-1 will operateproperly. In contrast, if a polar capacitor was used instead, thenconnector 435 would always need to be connected to the mating connector422 on the junction enclosure 420 in order to prevent damage to thecapacitors. As technicians may not appreciate that capacitors could bedamaged or destroyed if the jumper cable 430-1 were installed in thewrong direction, the use of non-polar capacitors 540 may preventinstallation errors and damage to the jumper cables. In someembodiments, at least two polar electrolytic capacitors may be usedinstead of a non-polar electrolytic capacitor.

The electrolytic capacitors 540 (or other capacitors used to implementthe shunt capacitance) may fail for a variety of reasons. For example,voltage surges resulting from, for example, lightning strikes may damagethese capacitors 540. Additionally, electrolytic capacitors may havedefects as manufactured that may not be identified during testing at thefactory but which may result in premature failure of the capacitor inthe field. The jumper cables according to some embodiments of thepresent invention may have circuitry that is designed to ensure, or atleast increase the likelihood, that if one of the capacitors 540 failsduring use, the capacitor 540 will exhibit an open circuit between thepower supply and ground conductors 432, 433. As long as such an opencircuit is presented, the jumper cable 430-1 will continue to performlike an ordinary jumper cable that does not include a shunt capacitanceunit 500. If the capacitors 540 fail to an open circuit, the jumpercable 430-1 may be more vulnerable to dI/dt voltage drops, but thejumper cable 430-1 will otherwise continue to operate and the failure ofthe capacitors 540 will not result in a general link failure.

In order to ensure that the capacitor 540, when it fails, will exhibitan open circuit between the supply and ground conductors 432, 433, afuse circuit 550 may be provided that creates an open circuit in theevent of failure of the capacitor 540. The fuse circuit 550 may beinternal to the capacitor 540 or may be a separate circuit that isexternal to the capacitor 540. In some embodiments, the fuse circuit 550may be implemented using a fuse 552 that is inserted along the shuntpath between the power supply and return conductors 432, 433. If thecapacitor 540 fails in a manner that results in a short circuit betweenthe power supply and return conductors 432, 433, the fuse 552 will“blow” (i.e., create an open circuit) in result to the increased currentacross the shunt path. The fuse 552 may be designed to conduct therelatively small currents that will flow through the capacitors 540 inresponse to a dI/dt voltage drop, but the fuse 552 will blow in responseto the much larger currents that will pass in the event that thecapacitors 540 fail and create a short circuit between the power supplyand return conductors 432, 433. The fuse circuit 550 may be anyappropriate circuit that creates an open circuit along the shuntcapacitance path in the event that the capacitors 540 fail in such amanner to create a short circuit between the power supply and returnconductors 432, 433.

FIG. 11C is a circuit diagram illustrating how the shunt capacitanceunit 500 is interposed between the power supply and return conductors432, 433. As shown in FIG. 11C, the capacitors 540-1 and 540-2 areconnected in series between the power supply conductor 432 and thereturn conductor 433. The fuse circuit 550 is located in series betweenthe capacitors 540-1 and 540-2. In other embodiments, the fuse circuit550 may be positioned, for example, between the power supply conductorand the first capacitor 540-1 or between the return conductor 433 andthe second capacitor 540-2.

FIGS. 12A and 12B are side views of capacitive-loaded jumper cables430-2 and 430-3 according to further embodiments of the presentinvention. As discussed above with reference to FIGS. 10, 11A and 11B,in some embodiments, the shunt capacitance unit 438 of jumper cable430-1 may be implemented as a sealed unit 500 that is interposed alongcable segment 431. As is schematically shown in FIG. 12A, in otherembodiments, jumper cables 430-2 may be provided in which the shuntcapacitance unit 438 may be implemented within the cable jacket 434 inorder to eliminate the need for the housing 510. In such embodiments,the cable jacket 434 may provide environmental protection to the shuntcapacitance unit 438. As is schematically shown in FIG. 12B, in stillfurther embodiments, jumper cables 430-3 may be provided in which theshunt capacitance unit 438 may be implemented within one of theconnectors 435, 436 of the jumper cable 430-3, which again eliminatesthe need for a separate housing 510. In such embodiments, the connectors435, 436 may provide environmental protection to the shunt capacitanceunit 438. In the jumper cables 430-2 and 430-3 of both FIGS. 12A and12B, the shunt capacitance unit 438 may have the circuit configurationillustrated in FIG. 11C.

It will also be appreciated that in still further embodiments, the shuntcapacitance unit may be implemented as a stand-alone unit that may beconnected, for example, between the junction enclosure 420 and aconventional jumper cable or between the remote radio head 440 and aconventional jumper cable. By way of example, FIG. 13 illustrates how astand-alone shunt capacitance unit may be provided in the form of aninline connector module 600 that may be connected between a conventionaljumper cable 430 and either the junction enclosure 420 or the remoteradio head 440. As shown in FIG. 13, the inline connector module 600includes a housing 610 and first and second connectors 620, 622. Theconnector 620 may be configured to connect to one of the connectors 435,436 of the conventional jumper cable 430 and the connector 622 may beconfigured to mate with a connector of the junction enclosure 420 or theremote radio head 440. Power supply and ground conductors 632, 633 maybe provided within the inline connector module 600, and a shuntcapacitance unit 640 may be provided that includes one or morecapacitors and, optionally, a fuse circuit, that are connected in seriesalong a shunt path between the power supply and ground conductors 632,633. The power supply and ground conductors 632, 633, and the capacitorsand the fuse circuit of the shunt capacitance unit 640 may beelectrically arranged with respect to each other as shown in the circuitdiagram of FIG. 11C.

As discussed above with reference to FIG. 9, in some embodiments, shuntcapacitance units may be used in cellular base stations that employprogrammable power supplies that are used to reduce the I*R voltage dropby maintaining the voltages of the power signals at the remote radioheads at or near a maximum voltage for the power signal that isspecified for each remote radio head. It will be appreciated that theshunt capacitance units may be implemented in the trunk cable, in thejumper cables, or using stand-alone units as discussed in the variousembodiments described above.

As is discussed in detail in the aforementioned '897 application, insome embodiments, the programmable power supplies may be configured tomeasure, estimate, calculate or receive the resistance of the powercabling connection that is interposed between the power supply and theremote radio head (this connection typically includes a trunk cable anda jumper cable). Pursuant to further embodiments of the presentinvention, the shunt capacitance units may be used to measure theimpedance of the power cabling connection.

In particular, FIG. 14 as a schematic block diagram illustrating how theshunt capacitance units according to embodiments of the presentinvention may be used to facilitate measuring the resistance of thepower cabling between the power supply and, for example, a remote radiohead. As shown in FIG. 14, a programmable power supply 700 may beprovided that delivers DC power to a remote radio head 760 over thepower supply and return conductors 751, 752 of a power cablingconnection 750. The power cabling connection 750 may comprise one ormore cables. For example, the power cabling connection 750 may comprisethe power supply portion of a trunk cable and a jumper cable that areconnected in series between the programmable power supply 700 and theremote radio head 760. As shown in FIG. 14, a shunt capacitance unit 753is provided along the power cabling connection 750 adjacent the remoteradio head 760. The shunt capacitance unit 753 may be implemented, forexample, in a jumper cable that connects the power supply and returnconductors of a trunk cable to the remote radio head 760.

The programmable power supply 700 includes a DC power generator 710 thatprovides a DC power signal that is used to power the remote radio head760. The programmable power supply 700 further includes a pulsegenerator 720 that is configured to generate an alternating current(“AC”) control signal that may also be transmitted onto the powercabling connection 750. This AC signal may be, for example, a 100 Hz to100 kHz voltage pulse. The frequency of the voltage pulse may beselected so that the voltage pulse will pass through the capacitors ofthe shunt capacitance unit 753. The frequency of the voltage pulse mayalso be selected to be lower than the RF data signals that aretransmitted by the remote radio head 760 to reduce or minimize anypotential interference between the voltage pulse and the RF datasignals.

As the shunt capacitance unit 753 will appear as a short circuit to thevoltage pulse, the voltage pulse will not pass to the remote radio head760, but instead will flow through the shunt capacitance unit 753 andback to the programmable power supply 700. Ohm's law may then be used todetermine the resistance of the power cable 750 based on thecurrent/voltage characteristics of the voltage pulse that is received atthe programmable power supply 700. The programmable power supply 700 mayinclude control circuitry 740 that is used to measure the voltage and orcurrent levels of the return voltage pulse and control logic 730 whichcalculates the resistance of the power cabling connection 750 basedthereon.

Thus, in the embodiment of FIG. 14, so long as the shunt capacitanceunit operates properly, it may be used as a bypass path for the voltagepulse in order to allow the programmable power supply 700 to measure theresistance of the power cable 750 and dynamically vary the output of thepower supply 700 based thereon. Moreover, if a capacitor in the shuntcapacitance unit 753 fails, the voltage pulse will no longer be receivedat the power supply 700, as the shunt capacitance unit 753 will fail toan open circuit. When this occurs, the power supply 700 may beconfigured to issue an alarm so that the shunt capacitance unit may bereplaced.

The present invention has been described with reference to theaccompanying drawings, in which certain embodiments of the invention areshown. This invention may, however, be embodied in many different formsand should not be construed as limited to the embodiments that arepictured and described herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout the specification anddrawings. It will also be appreciated that the embodiments disclosedabove can be combined in any way and/or combination to provide manyadditional embodiments. For example, the shunt capacitance unitsdescribed herein may be used in any of the example embodiments disclosedin the above-described '897 application.

It will be understood that, although the terms first, second, etc. areused herein to describe various elements, these elements should not belimited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

Unless otherwise defined, all technical and scientific terms that areused in this disclosure have the same meaning as commonly understood byone of ordinary skill in the art to which this invention belongs. Theterminology used in the above description is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the invention. As used in this disclosure, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will also beunderstood that when an element (e.g., a device, circuit, etc.) isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

It will be further understood that the terms “comprises” “comprising,”“includes” and/or “including” when used herein, specify the presence ofstated features, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,operations, elements, components, and/or groups thereof.

In the drawings and specification, there have been disclosed typicalembodiments of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being set forth inthe following claims.

That which is claimed is:
 1. A method of operating a cellular basestation, the method comprising: supplying a direct current (“DC”) powersignal from a power supply to a remote radio head that is mountedremotely from the power supply over a power cabling connection thatincludes a power supply conductor and a return conductor, the powercabling connection including a shunt capacitance unit coupled betweenpower supply conductor and the return conductor; transmitting analternating current (“AC”) control signal onto the power cablingconnection; receiving the AC control signal after it passes through theshunt capacitance unit; and determining a resistance or an impedance ofthe power cabling connection based on the received AC control signal. 2.The method of claim 1, wherein a frequency of the AC control signal isat least 100 Hertz.
 3. The method of claim 1, wherein a frequency of theAC control signal is at least 100 kilohertz.
 4. The method of claim 1,wherein the shunt capacitance unit is adjacent the remote radio head. 5.The method of claim 1, wherein determining the resistance or theimpedance of the power cabling connection based on the received ACcontrol signal comprises measuring at least one of a voltage level and acurrent level of the received AC control signal and calculating theresistance or impedance of the power cabling connection based on the atleast one measured voltage level and/or current level.
 6. The method ofclaim 1, wherein the AC control signal is generated by a pulse generatorof the power supply.
 7. The method of claim 1, wherein the power cablingconnection comprises a trunk cable and a jumper cable that are connectedin series,
 8. The method of claim 7, wherein the shunt capacitance unitis part of the jumper cable.
 9. The method of claim 1, wherein afrequency of the AC control signal is selected to be high enough so thatthe AC control signal will pass through the shunt capacitance unit. 10.The method of claim 9, wherein the frequency of the AC control signal islower than a transmission frequency of the remote radio head.
 11. Themethod of claim 1, wherein determining the resistance or an impedance ofthe power cabling connection based on the received AC control signalcomprises using Ohm's law to calculate the resistance or impedance ofthe power cabling connection based on the measured voltage level and/orcurrent level.
 12. The method of claim 1, wherein a frequency of the ACcontrol signal is between 100 Hertz and 100 kilohertz.